In the field of ellipsometry, the ratio (E.sub.p /E.sub.s).sup.r / (E.sub.p /E.sub.s).sup.i denoting the changes in the polarization state produced by the surface studied, is generally represented in the following form: tg.psi..exp(i.DELTA.)=(E.sub.p /E.sub.s).sup.r /(E.sub.p /E.sub.s).sup.i
The object of ellipsometry is therefore to measure the parameters .psi. and .DELTA. for a given surface.
It is thus possible, for example, to study the growth mechanisms of thin films and the formation of interfaces, and even to control a preparation process.
Ellipsometry is a non-destructive, non-interference-generating method of analysis. Measurements can therefore be taken in situ on samples under real conditions of preparation.
Depending on the wavelength domain of the source used (near ultraviolet, visible, near infrared, infrared), different properties of materials can be accessed or different materials scanned.
In the ultraviolet and visible domains, the penetration depth of the beam is often low. Such conditions are ideal for studying surfaces and interfaces, and for real time controls involving cleaning operations. It does not generally give access to the voluminal properties of materials, this being obtainable by measurements taken in the infrared domain.
Infrared is ideal for measuring such properties as vibrational absorption (chemical bonding).
The wavelength domain considered has a determining influence on the measuring devices and instruments used. In fact some components and techniques, known and usable in one wavelength domain, are not transposable or do not give sufficient precision in another.
In the infrared domain, i.e. for wavelengths between approximately 2 and 19 micrometers, different ellipsometers are known.
German patent DE-1572 19 describes a Fourier-transform ellipsometer. This device comprises a Michelson interferometer placed before or after the sample. The sample is placed between a polarizer and an analyzer which are both fixed in orientation during the taking of a measurement. In certain embodiments, a third polarizer is placed between the source and the input polarizer.
French patent FR-2 602 338 describes a phase-modulated ellipsometer comprising a diffraction grating monochromator.